Question: Compute $\frac{x^8+12x^4+36}{x^4+6}$ when $x=5$.
Solution: Note that $\left(x^4+6\right)^2=x^8+12x^4+36$. So $\frac{x^8+12x^4+36}{x^4+6}=\frac{\left(x^4+6\right)^2}{x^4+6}=x^4+6$. Our answer is therefore $5^4+6=625+6=\boxed{631}$.